The present invention relates to a method and apparatus for predicting a deformation amount in plastic injection molding and, more particularly, to a method and apparatus for predicting a deformation amount which are suitably applied to a simulation program that analyzes the behavior of a molten resin from injection into a mold to setting, and predicts a limit where a "warp" occurs in a plastic molded article, especially a thin molded article, which is obtained by removal after mold opening.
Conventionally, a simulation program is known which is used for predicting the behavior of a resin during resin injection molding and a warp deformation in a plastic molded article. According to this program, when calculation of the resin behavior and prediction of a warp are to be performed, the model shape of a plastic molded article is created. The model shape is divided into meshes to enable calculation of the finite element method. Various molding conditions are input as boundary conditions, and various material data of the resin are input. When a plastic resin in a molten state is to be filled into the cavity of a mold without a gap, the equation of motion, the equation of energy conservation, and the equation of continuity are formulated by the finite element method, thereby predicting the behavior of the molten resin.
In the packing and cooling processes of the mold after the resin is filled, in order to further consider the compression properties of the resin, the volume shrinkage factor is finally calculated based on an equation of P (Pressure)-V (Volume ratio)-T (Temperature), thereby calculating uniform shrinkage factors in the x, y, and z directions, i.e., a direction of thickness and planar directions.
The distribution of the shrinkage factors within the surface finally obtained in this manner is recognized and input as an initial strain in advance. The warp deformation in the plastic molded article is predicted from a calculation result obtained by an injection molding predicting method formulated in accordance with the finite element method.
One of the greatest features of a plastic molded article is the anisotropy of the shrinkage factor. Especially, it is known that in a thin molded article, the shrinking behaviors largely differ between the direction of thickness and the planar directions.
Furthermore, it is conventionally known by the skilled in the art from experiences that the shrinking behaviors greatly differ between in the direction of the resin flow in the planar directions and in a direction perpendicular to this direction of the resin flow.
In the conventional simulation program, however, the behavior of the anisotropy of the shrinkage factor is not considered. More specifically, according to the conventional simulation program, a volume shrinkage factor is simply equally divided into x, y, and z directions, and the divided factor components are distributed to the direction of thickness and the planar directions, thereby obtaining a shrinkage factor. Then, a warp deformation in an injection-molded article is predicted by utilizing the shrinkage factor components in the planar directions as the initial strains. As a result, higher-precision warp prediction cannot be performed.